Consumable Electrode Type Welding Method

ABSTRACT

In a conventional consumable electrode type welding method, owing to the need of the reversing operation of a robot manipulator, an extra response time as well as acceleration and deceleration times are necessary and, at the same time, the feed speed of a welding wire is not be able to catch up with the melting speed of the welding wire to thereby extend the length of an arc, resulting in the unstable arc. In a consumable electrode type welding method according to the invention, while feeding a welding wire  1,  a welding torch  4  is moved by a robot manipulator  9  in a direction where the welding torch  4  is pulled apart from a base metal  7,  so that an initial arc is generated while the welding wire  1  is separated from the base metal  7.  This not only can eliminate the need for the reversing operation of the robot manipulator  9  and thus can reduce the waste time to thereby be able to reduce a tact time but also can stabilize an arc in the welding start portion and thus can reduce the “unexpected stop” effectively.

FIELD OF THE INVENTION

The present invention relates to a consumable electrode type weldingmethod for generating an arc between a welding wire serving as aconsumable electrode and a welding base metal serving as a member to bewelded to thereby control the welding output.

BACKGROUND OF THE INVENTION

Recently, the welding industry has always made effort to further enhancethe productivity of the welding operation in order to secure aninternational competitive ability.

Especially, there have been increasing the need for a reduction in a socalled “unexpected stop”, which is a slight trouble causing theproduction line to stop, and the need for a reduction in the tact timemore than before.

As the reasons for the unexpected stop, there can be pointed out variousreasons and the greatest reason is a trouble caused by fault in an arcstart.

In view of this, in a conventional consumable electrode type weldingmethod, as a method for enforcing its arc start, there is known thefollowing method: that is, when a start signal is input from theoutside, a robot manipulator is moved to thereby move a welding torch toa previously instructed welding start position and after then, while thefeeding of the welding wire remains stopped, the welding torch is movedsubstantially in the welding wire feed direction by the robotmanipulator to thereby allow the leading end of the welding wire toapproach the member to be welded; if it is detected that the weldingwire leading end has come into contact with the member to be welded, aninitial current of a preset small current value is applied from awelding power supply device and, at the same time, the welding torch ismoved in the opposite direction to the substantially welding wire feeddirection to thereby carry out the retreating movement of the weldingtorch which moves the welding wire leading end away from the member tobe welded; if the welding wire leading end and the member to be weldedare moved away from each other due to the retreating movement of thewelding torch, there is generated an arc to which the initial current isapplied and, while the initial arc generating state remains held, theretreating movement of the welding torch is allowed to continue; if thewelding torch returns back to the welding start position, the retreatingmovement is switched over to the movement in the previously instructedwelding direction and, at the same time, the feed of the welding wire isstarted and a steady-state welding current is applied, whereby theinitial arc generating state is switched over to the steady-state arcgenerating stage. (For example, see the patent literature 1).

Now, FIG. 5 is a schematic block diagram of the whole of a weldingsystem for enforcing the above-mentioned consumable electrode typewelding method using a robot.

In FIG. 5, reference character 101 designates a welding wire used as aconsumable electrode; and, the welding wire 101 can be played out from awire spool 102 in the direction of a welding torch 104 by a wire feedmotor 103. Reference numeral 105 stands for a welding power supplydevice. The welding power supply device 105 applies a given weldingcurrent I and a given welding voltage V, through the welding torch 104and welding tip 106, into between the welding wire 101 and a base metal107 serving as a member to be welded to thereby generate an arc 108 andcontrol the wire feed motor 103 for enforcing the welding operation.

Reference numeral 109 designates a robot manipulator. The robotmanipulator 109 holds the welding torch 104, positions the torch 104 ata welding start position (not shown) and moves the welding torch 104along a welding line (not shown).

Also, the robot manipulator 109 is controlled by a robot control unit110. The robot control unit 110 executes a two-way communication Sbetween the welding power supply device 105 and itself and thus therobot control unit 110 sends welding conditions such as the weldingcurrent I and welding voltage V as well as instruction signals such as awelding start signal and a welding end signal.

Now, description will be given below of a consumable electrode typewelding method used in the above-structured system with reference to atiming chart shown in FIG. 6.

Referring to FIG. 6 specifically, in the vertical direction thereof,there are shown the respective states of the moving speed of the weldingtorch TV, the feeding speed of the welding wire WF, a short circuitdetect signal A/S, a welding current I and a welding voltage V, whereasthe horizontal axis thereof expresses time. In this illustration, astimings, TS0 designates a timing when a welding start signal istransmitted from the robot control unit 110 to the welding power supplydevice 105, while TS1 - TS5 following TSO stand for timings in thecourse of time respectively.

Firstly, the robot control unit 110 not only transmits a welding startsignal to the welding power supply device 105 but also actuates therobot manipulator 109 to accelerate the welding torch 104 toward thebase metal 107. And, when the speed of the welding torch 104 reaches aninitial torch speed TV0, the robot control unit 110 causes theacceleration of the robot manipulator 109 to stop and continues thelowering motion of the welding torch 104 at a constant speed.

Also, when receiving the welding start signal from the robot controlunit 110, the welding power supply device 105 applies a no-load voltageVO into between the welding wire 101 and base metal 107.

Then, at the timing TS1, if the welding wire 101 is contacted with thebase metal 107, short circuit detect means (not shown) provided in theinside of the welding power supply device 105 outputs a short circuitsignal A/S.

This short circuit detect signal A/S is transmitted through the two-waycommunication S to the robot control unit 110 and thus the robot controlunit 110 reduces and stops the robot manipulator 109 immediately, sothat, at the timing TS2, the operation of the robot manipulator 109 iscaused to stop, that is, the speed of the welding torch 104 becomeszero.

After then, the robot control unit 110 immediately reverses theoperation of the robot manipulator 109 and starts the operation thereofin a direction where the welding torch 104 is pulled apart from the basemetal 107, thereby lifting the welding torch 104.

The period extending from the timing TS1 to TS3 is a short circuitperiod and, in this period, during the time until the timing TS2 wherethe robot manipulator 109 reduces down to zero, the welding wire 101 ispressed against the base metal 107; but, from the timing TS2 on, sincethe operation of the robot manipulator 109 is reversed, the pressingamount of the welding wire 101 decreases and thus, at the timing TS3,the short circuit is removed.

The timing, that is, the timing TS3 occurs at the time when the area ofa triangle cde, which is shown by the line of the speed TV of thewelding torch and expresses the lifting amount of the welding wire 101,exceeds the area of a triangle abc which is shown by the line of thespeed TV of the welding torch for expressing the pressing amount of thewelding wire 101.

Here, when the initial short circuit occurs at the timing TS1, thewelding power supply device 105 controls the welding current I at I1,and then increases the current up to I2 after passage of a given timeand waits for the opening of the short circuit.

As the first stage of the initial short circuit period, the weldingcurrent is controlled to I1 which is set relatively low. The reason forthis is to avoid a possibility that, owing to the initial short circuit,the leading end portion of the welding wire is heated due to Jouleeffect to melt the wire and thus, simultaneously with generation of thearc, the molten welding wire can spatter around to form spatters.

Also, to change the current from I1 to I2 is to be able to apply energyenough to generate the arc when the short circuit is opened at thetiming TS3.

When an arc is generated at the timing TS3, the welding power supplydevice 105 actuates the wire feed motor 103 to accelerate the weldingwire 101 toward the base metal 107, continues the acceleration until thespeed of the welding wire 101 reaches a welding wire speed (not shown)for actual welding, and, after the welding wire speed reaches thewelding wire speed for actual welding, continues the feeding of thewelding wire at a constant speed.

Also, after controlling the arc current I to an arc initial current I3′for a given time in linking with the actuation of the wire feed motor103, the welding power supply device 105 controls the current to asecond initial current I4 and, after then, controls the current to anoutput for actual welding (not shown).

Next, description will be given below of a welding end time in theabove-mentioned consumable electrode type welding method in the weldingsystem with reference to a timing chart shown in FIG. 7.

Referring to FIG. 6 specifically, in the vertical direction thereof,there are shown the respective states of the moving speed of the weldingtorch TV, the feeding speed of the welding wire WF and a welding outputP, whereas the horizontal axis thereof expresses time. In thisillustration, as timings, TEO designates a timing when a welding endsignal is transmitted from the robot control unit 110 to the weldingpower supply device 105, while TE1-TE4 following TEO stand for timingsin the course of time respectively.

Firstly, when receiving a welding end signal from the robot control unit110, the welding power supply device 105 controls the wire feed motor103 to reduce the feed speed of the welding wire 101.

Simultaneously with this feed speed reduction of the welding wire, thewelding power supply device 105 reduces the welding output and, at atiming TE2′ where a predetermined condition is satisfied, it controlsthe welding output to a constant welding output.

This constant output PI is referred to as a “burn-back”. Generally, thewelding power supply device 105 continues the burn-back at and from atiming TE3′ where the welding wire 101 is caused to stop, that is, keepsthe constant output to continue the ark 108 for a given period; and,after the welding wire 101 is burned up, the welding power supply device105 stops the constant output at a timing TE4′.

This “burn-back” control method is a widely used control method forpreventing occurrence of a so called wire stick phenomenon in which thewelding wire 101 is contacted with a molten pool (not shown) and isthereby fixed when the welding is ended.

Patent literature: JP 2002-205169 publication

DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

However, the conventional consumable electrode type welding methodrequires the reversing operation of the robot manipulator 109.

That is, when it is detected that the leading end of the welding wire101 is contacted with the base metal 107, the reduction of the speed ofthe robot manipulator 109 moving forwardly is started, the forwardmovement of the robot manipulator 109 is the caused to stop once, and,after then, the operation of the robot manipulator 109 is reversed andaccelerated in the backward direction, which requires not only theresponse time of the robot manipulator 109 but also the acceleration andreduction times thereof.

Also, since the wire feed motor 103 is actuated for the first time aftergeneration of the initial arc, the feed of the welding wire 101 is notbe able to catch up with the melting speed of the welding wire 101 tothereby extend the length of the arc 108, resulting in the unstable arc108.

And, in the welding end time, to prevent the “wire stick” phenomenon,there is necessary the “burn-back” processing, which takes time forexecution of this processing, so that the tact time is extended. Also,there is formed a ball-like fixed body in the leading end of the weldingwire 101 due to the burnt-up of the welding wire 10, which obstructs thearc start in the next step.

Thus, it is an object of the invention to provide a consumable electrodetype welding method which can reduce the waste time found in theconventional consumable electrode type welding method, can hold theproper length of an arc after generation of the arc to thereby stabilizethe arc in the welding start part, and can positively prevent theoccurrence of the wire stick phenomenon and can hold the wire leadingend portion in a proper shape, thereby being able to carry out a properarc start in the next step.

MEANS FOR SOLVING THE PROBLEMS

In attaining the above object, according to the invention, there isprovided a consumable electrode type welding method in which, using awelding system comprising wire feed means for feeding a welding wire toa welding torch, an actuator for holding the welding torch and movingthe welding torch, a control unit for driving and controlling theactuator, and a welding power supply device for applying a weldingoutput into and between a member to be welded and the welding wire, thewelding torch is moved by the actuator in a direction where the weldingtorch is pulled apart from the member to be welded while feeding thewelding wire to thereby control the speed of the welding wire withrespect to the member to be welded.

According to this method, since the actuator can control the speed ofthe welding wire with respect to the member to be welded through aone-way operation, the response time and acceleration/reduction time canbe reduced when compared with the conventional method, and also becausethe distance between the welding wire and the member to be welded can becontrolled with a good following capability, an arc can be stabilizedearly.

Also, the “burn-back” processing time in the welding end time can alsobe reduced when compared with the conventional method.

EFFECTS OF THE INVENTION

As described above, according to the invention, since, while feeding thewelding wire, the actuator moves the welding torch in a direction wherethe welding torch is pulled apart from the welding wire to thereby allowan initial arc to occur with the welding wire separated from the memberto be welded, not only the reversing operation is eliminated and thusthe waste time is reduced to be thereby able to reduce the tact time,but also the arc in the welding start time can be stabilized to therebyreduce the “unexpected stop” effectively.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment

Now, description will be given below of an embodiment of a consumableelectrode type welding method according to the invention with referenceto FIGS. 1 to 4.

FIG. 1 is a schematic block diagram of the outline of a welding systemfor enforcing the invention, in which reference character 1 designates awelding wire used as a consumable electrode to be played out in thedirection of a welding torch 4 from a wire spool 2 by a wire feed motor3. stands for a welding power supply device which applies a givenwelding current I and a given welding voltage V, through the weldingtorch 4 and a welding tip 6, into between the welding wire 1 and a basemetal 7 used as a member to be welded to generate an arc and alsocontrols the wire feed motor 3, thereby enforcing the welding operation.

9 designates a robot manipulator which holds the welding torch 4,positions the welding torch 4 at a welding start position (not shown),and moves the welding torch 4 along a welding line (not shown).

Also, the robot manipulator 9 is controlled by a robot control unit 10.The robot control unit 10 executes a two-way communication S between thewelding power supply device 5 and itself and transmits weldingconditions such as the welding current I and welding voltage V as wellas welding start and end instructions.

Referring to FIG. 2, in the vertical direction thereof, there are shownthe respective states of the moving speed of the welding torch TV, thefeed speed of the welding wire WF, short circuit detect signal A/S,welding current I and welding voltage, whereas, in the horizontal axisthereof, there is shown time. As timings, TS0 designates a timing wherea welding start signal is transmitted from the robot control unit 10 tothe welding power supply device 5, while TS1-TS5 respectively expresstimings following TS0.

In FIG. 2, according to the present embodiment, when the welding startsignal is transmitted from the robot control unit 10 to the weldingpower supply device 5 (TS0), the welding power supply device 5 applies ano-load voltage V0 into between the welding wire 1 and base metal 7 andalso actuates the wire feed motor 3 to thereby accelerate the weldingwire 1 toward the base metal 7.

When the feed speed of the welding wire 1 reaches an initial wire speedW0, the welding power supply device 5 causes the wire feed motor 3 tostop the acceleration of the welding wire but continues the wire feed ata constant speed.

Then, at the timing TS1, when the welding wire 1 is contacted with thebase metal 7, a short circuit signal A/S is output from short circuitdetect means (not shown) which is provided in the inside of the weldingpower supply device 5.

The short circuit detect signal A/S is transmitted through the two-waycommunication S to the robot control unit 10. The robot control unit 10immediately actuates the robot manipulator 9 to start to move thewelding torch 4 in a direction where the welding torch 4 is pulledsubstantially apart from the base metal 7 and also to lift the weldingtorch 4.

A period from TS1 to TS3 is a short circuit period and, during thisperiod, the welding wire 1 is continuously fed at an initial wire speedW0 and the robot manipulator 9 continues to lift the welding torch 4.Therefore, the speed of the leading end portion of the welding wire 1 isa composite speed of the wire speed WF and torch speed TV as shown by abroken line in FIG. 2.

Thus, the leading end of the welding wire 1, at and after TS1, causesthe welding wire 1 to be pressed against the base metal until TS2 wherethe composite speed shown by a broken line in FIG. 2 becomes zero; atand after TS2, the composite speed turns to a negative speed and thusthe pressing amount decreases; and, at the timing TS3, the short circuitis opened. The timing TS3 occurs at the time when the wire liftingamount, that is, the area of a triangle hji exceeds the wire pressingamount or the area of a triangle fgh.

By the way, when an initial short circuit occurs at the timing TS1, thewelding power supply device 5 controls the welding current I to turn toI1 and, after passage of a given time, increases the current up to I2and waits for the opening of the short circuit.

The reason why the welding current is controlled to I1 set relativelylow as the first stage of the initial short circuit period is to preventoccurrence of a phenomenon that the wire can be molten due to the Jouleheat of the wire leading end portion caused by the initial short circuitand thus the molten wire can spatter around simultaneously withgeneration of an arc.

Also, the reason why the welding current is varied from I1 to I2 is tobe able to provide sufficient energy to generate an arc when the shortcircuit is opened at the timing TS3.

Now, FIG. 3 is an explanatory timing chart in which the wire speed WFaccording to the prior art shown by a broken line is overlapped on thesame timing chart as shown in FIG. 2 according to the presentembodiment, in order to be able to compare the invention with the priorart.

As can be seen clearly from FIG. 3, in the arc start according to theprior art, at the time when the short circuit is opened and an arc isgenerated at the timing TS3, the welding wire starts to accelerate forthe first time. Therefore, for example, if the timings of the inventionand prior art when the wire speed becomes WF4 are compared with eachother, the prior art method is found slower by the time from TS4 toTS4′.

As described above, according to the present embodiment, when it isdetected that the leading end of the welding wire 1 comes into contactwith the base metal 7 used as the member to be welded, by lifting thewelding torch 4 using the robot manipulator 9 while continuing theforward feed of the welding wire 1, an arc is generated in a state wherethe welding wire 1 is separated from the base metal 7. Owing to this,not only the reverse operation of the robot manipulator is eliminated tothereby be able to reduce the waste time and thus the tact time but alsoan arc in the welding start end portion can be stabilized and thus the“unexpected stop” can be reduced effectively.

Next, description will be given below of an embodiment of an arc endaccording to the invention with reference to a timing chart shown inFIG. 4.

By the way, in FIG. 4, in the vertical direction thereof, there areshown the respective states of the moving speed of the welding torch TV,the feed speed of the welding wire WF and welding output P and, in thehorizontal axis thereof, there is expressed time; and, as timings, thetime when a welding end signal is transmitted from the robot controlunit 10 to the welding power supply device 5 is expressed as a timingTE0, while TE1-TE4 respectively express timings following the timingTE0.

According to the present embodiment, on receiving the welding end signalfrom the robot control unit 10, the welding power supply device 5controls the wire feed motor 3 to reduce the speed of the welding wire.

In linking with the speed reduction of the welding wire, the weldingoutput is also reduced and, at the timing TE1 where a predeterminedcondition is satisfied, the welding power supply device 5 transmits astart signal for lifting the welding torch 4 to the robot control unit10.

On receiving the lifting operation start signal from the welding powersupply device 5, the robot control unit 10 immediately controls therobot manipulator 9 to lift the welding torch 4.

As a result, the speed of the leading end of the welding wire 1 becomesa composite speed of the wire speed WF and torch speed TV, that is, itbecomes such speed as shown by a broken line in FIG. 4.

Thus, at the timing TE2, the speed of the welding wire 1 becomes zerowith respect to the base metal 7, thereby being able to stop the weldingoutput P.

From that time on as well, the operation of the welding wire 1 and thelifting operation of the welding torch 4 are executed continuously but,at the time when the area of a trapezoid klmn, which corresponds to thelifting distance of the welding torch 4, exceeds the area of a triangleopq corresponding to the inertial running distance of the welding wire 1until it stops, there is eliminated a danger of the wire stickphenomenon in which the welding wire 1 is contacted with the molten poolof the base metal 7 and is thereby fixed. Therefore, the robot controlunit 10 immediately controls the robot manipulator 9 so as to be able toswitch over to a next operation (for example, an operation in which themanipulator 9 moves to the position of the welding torch at the weldingstart time for a next welding operation).

As described above, according to the present embodiment, since there iseliminated the time conventionally necessary for the “burn-back”operation, the tact time can be reduced quite effectively; and also,since there is prevented formation of a large ball-like fixed body inthe leading end of the welding wire 1 due to the burn-up of the weldingwire, there can be avoided an ill influence on the welding start for thenext step.

By the way, in the present embodiment, the lifting operation of thewelding torch is carried out by the robot manipulator. However, theremay also be provided an actuator separately and the lifting operation ofthe welding torch may be executed using this 5 actuator. And, in thiscase, without using a robot, for example, using an automatic machine,the welding torch may be positioned or may be moved along a weldingline, which, of course, has no ill influence on the effects of theinvention.

INDUSTRIAL PRACTICABILITY

A consumable electrode type welding method according to the inventionnot only can eliminate the need for the reverse operation of the robotmanipulator to reduce the waste time to thereby be able to reduce thetact time but also can stabilize an arc in the welding start portion andreduce the “unexpected stop” effectively. Therefore, the invention isindustrially useful as a consumable electrode type welding method whichis used, for example, in production facilities and construction work.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a welding system for use in anembodiment according to the invention.

FIG. 2 is a timing chart for an arc start time in an embodimentaccording to the invention.

FIG. 3 is a timing chart for an arc start time used to compare theembodiment according to the invention with a prior art technology.

FIG. 4 is a timing chart for an arc end time in an embodiment accordingto the invention.

FIG. 5 is a schematic block diagram of a welding system used in a priorart technology.

FIG. 6 is a timing chart for an arc start time in a prior arttechnology.

FIG. 7 is a timing chart for an arc end time in a prior art technology.

DESCRIPTION OF REFERENCE CHARACTERS

-   1: Welding wire-   3: Wire feed motor-   4: Welding torch-   5: Welding power supply device-   7: Base metal-   8: Arc-   9: Robot manipulator-   10: Robot control unit

1. A consumable electrode type welding method in which, using a weldingsystem comprising wire feed means for feeding a welding wire to awelding torch, an actuator for holding and moving the welding torch, acontrol unit for driving and controlling the actuator, and a weldingpower supply device for applying a welding output into between a memberto be welded and the welding wire, the method comprising the steps of:moving the welding torch by the actuator in a direction parting awayfrom the member to be welded while feeding the welding wire; andcontrolling the speed of the welding wire with respect to the member tobe welded.
 2. A consumable electrode type welding method as set forth inclaim 1, wherein, at a welding start time, firstly, the welding wire isfed while the actuator is stopped and, after the welding wire iscontacted with the member to be welded, while applying a welding output,the welding torch is pulled apart from the member to be welded at aspeed equal to or higher than the feed speed of the welding wire by theactuator.
 3. A consumable electrode type welding method as set forth inclaim 2, wherein, at a welding start time, firstly, while the actuatoris stopped, the speed for feeding the welding wire is set equal to orlower than the feed speed of the welding wire in a normal welding timeand, after the welding torch is pulled apart from the member to bewelded, the feed speed of the welding wire is changed to the feed speedof the welding wire in the above normal welding time.
 4. A consumableelectrode type welding method as set forth in claim 2, wherein, aftercontact of the welding wire with the member to be welded, while applyingthe welding output, the welding torch is pulled apart from the member tobe welded to a given distance at the speed equal to or higher than thefeed speed of the welding wire by the actuator and, after then, themovement of the welding torch in the pull-apart direction is caused tostop.
 5. A consumable electrode type welding method as set forth inclaim 1, wherein, in a welding end time, while reducing the feed speedof the welding wire as well as the welding output, the welding torch ispulled apart from the member to be welded at a speed equal to or higherthan the feed speed of the welding wire by the actuator and, at a timingwhere the feed speed of the welding wire balances substantially with themoving speed of the actuator, the welding output is caused to stop.
 6. Aconsumable electrode type welding method as set forth in claim 5,wherein, at least until the feed speed of the welding wire reaches zero,the welding torch is moved by the actuator in a direction where it ispulled apart from the member to be welded.
 7. A consumable electrodetype welding method as set forth in claim 5, wherein, until the leadingend position of the welding wire reaches a distance between the weldingwire leading end and the member to be welded in the welding start time,the welding torch is pulled apart from the member to be welded by theactuator.